This invention relates to a process for converting biomass or cellulose material and in particular to converting-wood waste of various types into liquid hydrocarbons and in particularly acetic acid.
Our civilization has been burdened with the products of modem living since the industrial revolution began. It has resulted in the defilement of the environment, and even natural product residues have contributed to the problems we now face.
For example, there has been over the years an accumulation of piles of wood waste from logging operations and the production of laminates, plywoods, furniture, dimensional lumber for buildings, and pallets. The pulp and paper industry can only utilize specific parts of a tree and therefore leaves considerable residue that to date has little use.
In addition to xe2x80x9ccleanxe2x80x9d wood residues, there are many other types of wood residues which contain, or are coated with, paints, varnishes and chemicals: for example, demolished buildings or used and discarded wood from any source. These are more toxic to the environment because their on-board chemicals leach into the ground on which they sit.
The wood industry is very busy trying to find ways to utilize wood waste. A common alternate to landfill disposal is burning. Recently the industry has been focussing on using the heat from combusting wood waste to generate synthesis gas (syngas). Syngas is used to generate steam which is used to produce electrical power. But there is a disadvantage seldom emphasized, i.e. the large quantities of carbon dioxide produced and emitted into the atmosphere.
In addition, secondary industries have arisen to utilize wood waste, and these are the producers of particleboards, fiberboards, waferboards and extruded products. Other processes make animal bedding, animal litter, landscaping mulches, compost or ground covers. Some waste goes to erosion control.
Only a small percentage of wood waste is processed by the chemical industry. Some is used to produce methanol. Others utilize bacterial fermentation as a means of modifying wood residues into usable chemicals. These processes are relatively inefficient, with only the by-products of bacterial metabolism recovered. Enzymatic degradation of organic matter is a newer method to decompose the wood, but the economic viability of the process may be less than rewarding.
Accordingly, there exists a real need to utilize the cellulose waste to economically produce useful chemicals. Cellulose lends itself to reforming into the raw materials for plastics. Plastics are currently made using raw materials derived from petrochemical sources. In fact, we have relied heavily on the petrochemical industry to supply these raw materials. An efficient process to provide substantial volumes of these materials would have immediate positive impact on the world petrochemical industry. If indeed these materials could be produced at a lower cost, then not only would natural petroleum reserves be extended, but the economies of the plastic industry would shift in favour of the consumer.
A product with an extremely large world market such as acetic acid, would therefore be dramatically more lucrative than, for example, methanol since it is a raw material for the plastics industry. Additionally, chemical production with minimal greenhouse gas emissions would not only be economically more desirable, but environmentally more desirable. If wood waste is used to make raw materials for plastics, then the environment would be cleaned up and the world petroleum reserves would last longer.
A process for the production of acetic acid and other liquids from cellulose is disclosed. The cellulose is steam-gasified in the absence of air and the products consisting primarily of carbon monoxide and hydrogen are subjected to heat, pressure, and catalysts to form methyl alcohol. The methyl alcohol is mixed with carbon monoxide and subjected to heat, pressure and catalysts to form acetic acid and other liquids.
Additional carbon monoxide and hydrogen are generated from the burners using natural and unwanted process gas, under starved oxygen conditions, to provide heat for the gasifiers and additional feedstock for the conversion process. These gases are also added to the gases emerging from the gasification of the cellulose.
The carbon monoxide and hydrogen gases needed to make methyl alcohol and oxygenated C2 products are, firstly separated in molecular sieves, secondly metered into the pressure vessels in the correct ratios to form the products. Small amounts of mixed hydrocarbon gases (CxHy) are also removed by the molecular sieves, and sent back to the burners to supplement the heating gas.
In a further enhancement of the process, carbon and fly ash particles are filtered from the gas stream after steam gasification of the cellulose, and heated with steam in the presence of a catalyst, to form carbon monoxide and hydrogen. These gases are sent to the molecular sieves to be separated, and used subsequently in the pressure vessels to add to the products formed.
The final product liquid is run through an oil/water separator to remove water, then sent to a distillation tower where it is purified and removed from the system for sale. Any extraneous hydrocarbons which emerge from the distillation process, most of which is formed in the first pressure vessel, are sent back to the initial reactor to be re-processed with new cellulose input.
The three input gas streams arising from: 1) the steam gasification of cellulose; 2) the water/gas shift in the carbon reactor; and 3) the sub-stoichiometric oxygen burning of input burner gas to heat both retorts, maximize the output chemical production while reducing the consumption of energy needed for processing the cellulose and the carbon.
Further features of the invention will be described or will become apparent in the course of the following detailed description.